The present invention generally relates to improved medical devices and their use. More particularly, the present invention relates to an annular ring or an annuloplasty ring that is timely expandable for correction of certain disorders in the heart valves, blood vessels or other body conduits in a patient.
The human""s circulatory system consists of a heart and many blood vessels. In its path through the heart, the blood encounters four valves. The valve on the right side that separates the right atrium from the right ventricle has three cusps and is called the tricuspid valve. It closes when the ventricle contracts during a phase known as systole and it opens when the ventricle relaxes, a phase known as diastole. The pulmonary valve separates the right ventricle from the pulmonary artery. The mitral valve, so named because of its resemblance to a bishop""s mitre, is in the left ventricle and it separates the left atrium from the ventricle. The fourth valve is the aortic valve that separates the left ventricle from the aorta. In a venous circulatory system, a venous valve is to prevent the venous blood from leaking back into the upstream side so that the venous blood can return to the heart and consequently the lungs for blood oxygenating and waste removing purposes.
In many patients who suffer from diseased or congenitally dysfunctional cardiovascular tissues, a medical implant may be used to correct the problems. A dysfunctional heart valve hinders the normal functioning of the atrioventricular orifices and operation of the heart. More specifically, defects such as narrowing of the valve stenosis or a defective closing of a valve, referred to as valvular insufficiency, result in accumulation of blood in a heart cavity or regurgitation of blood past the valve. If uncorrected, prolonged valvular insufficiency may cause eventually total valve replacement. On the other hand, certain diseases cause the dilation of the heat valve annulus. Dilation may also cause deformation of the valve geometry or shape displacing one or more of the valve cusps from the center of the valve. Dilation and/or deformation result in an ineffective closure of the valve during ventricular contraction, which results in regurgitation or leakage of blood during contraction.
It is known to use annuloplasty ring in the repair of diseased or damaged atrioventricular valves that do not require replacement. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity in systole while permitting good hemodynamics in diastole. The annuloplasty ring also provides support for the mitral or tricuspid annulus and restricts expansion of the annulus or portions of the annulus to preset limits. A variety of annuloplasty rings have been employed, ranging from rigid rings of fixed sizes to flexible rings with a degree of adjustability. Obviously, annular prostheses that are of rigid fixed size must be carefully selected and skillfully sutured in place. Thus, an imperfect fit may require corrective surgery to replace the improperly implanted prosthesis. A rigid ring also prevents the normal flexibility of the valve annulus and has a tendency of sutures tearing during the normal movement of the valve annulus. Examples of rigid or partially rigid annuloplasty rings are disclosed in U.S. Pat. No. 5,061,277 (to Carpentier et al.) and in U.S. Pat. No. 5,104,407 (to Lam et al.).
Over the years flexible annuloplasty rings are designed and developed to overcome the problems of rigid rings and/or fixed size. One problem associated with the fixed size annuloplasty rings of the prior art is that, when such annuloplasty rings are implanted into children, the subsequent growth of the patient may render the annuloplasty ring too small for its intended function. Thus, follow-up surgery may be necessary to replace the originally implanted annuloplasty ring with a larger ring suitable for the thencurrent size of the patient.
Carpentier et al., in U.S. Pat. No. 5,593,435 and U.S. Pat. No. 5,888,240 describes an annuloplasty ring which is constructed and equipped for post-implantation size adjustment in situ to accommodate changes in annular size due to growth of the patient. It is disclosed that a distensible annuloplasty ring may be made up of a plurality of separate segments which are slidably or movably secured to one another to form a ring. It is also disclosed that when dilatory or outward pressure is exerted against the inner surface of the ring, as may be accomplished by way of a radially expandable balloon introduced within the annulus of the remodeled valve, such pressure will cause the segments to slide or distend relative to one another. However, such mechanical sliding or distension of the segments expands the circumference of the ring by an incremental increase at only a few joint points where any two slidable segments meet. By distending an incremental strain and simultaneously loading most of the distension stress at a few joint points, the overall shape of the annulus may be distorted. Furthermore, the intended valve functionality with that unevenly distended annuloplasty ring after a period of tissue ingrowths into and/or encapsulation onto the annuloplasty ring may be compromised.
Cardiovascular stents have been developed and used widely. A stent is a generally longitudinal tubular mesh-like device formed of biocompatible material, preferably a metallic or a plastic material, which is useful in the treatment of stenosis, strictures or aneurysms in body conduits such as blood vessels or around a valvular annulus. When a stent is expanded and enlarged, the whole section is expanded at essentially the same degree of extension. Special features of the stent configuration may include radially expandable non-axial contraction and/or spirals as disclosed in U.S. Pat. No. 6,042,606 (to Frantzen) and U.S. Pat. No. 6,033,433 (to Ehr et al.).
Balloon-assisted radial expansion for an expandable annuloplasty ring might restrict the blood flow undesirably. Radial mechanical force as disclosed in the prior art to expand an annuloplasty ring at a later time might not evenly expand the ring radially. Shape-memory material has been disclosed and widely used that it will return to its preshape when it is activated by heat or other suitable means. The shape-memory material may include plastic material, metal, and the like. For example, U.S. Pat. No. 5,163,952 (to Froix), U.S. Pat. No. 5,258,020 (to Froix), and U.S. Pat. No. 5,607,467 (to Froix) all disclose shape-memory plastic while U.S. Pat. No. 6,077,298 (to Tu et al.) discloses a shape-memory metallic device. The entire contents of these patents are incorporated herein by reference.
Therefore, it would be desirable to provide a radially expandable annuloplasty ring that has uniformly distending properties circumferentially to conform to the natural growth of the valve annulus of the patient without suffering the above-discussed disadvantages of localized stress at only a few joint points where any two slidable segments meet. The improved annuloplasty ring may be preferably evenly expanded by non-mechanical means, such as shape-memory mechanisms.
In general, it is an object of the present invention to provide an expandable annuloplasty ring which may be radially expanded in situ by way of a non-mechanical expandable means. It is another object of the present invention to provide an expandable annuloplasty with essentially uniform ring distension in the circumferential direction for each expansion process. It is still another object of the present invention to provide a method for expanding the radially expandable annuloplasty by expanding means for radially expanding the annuloplasty ring to a size larger than the prior size. It is a further object of the present invention to provide expanding means including heating a shape-memory material.
In accordance with one embodiment of the invention, the annuloplasty ring may be made up of a fabric sheath, and at least one stenting element mounted within the fabric sheath, wherein the at least one stenting element is made of shape-memory material. The shape-memory material has a preshape and a shape-transition temperature, wherein the shape-memory material expands to its preshape so as to expand the annuloplasty ring when the shape-memory material is heated to above the shape-transition temperature. In one embodiment, the annuloplasty ring so formed is a completely close ring while in an alternative embodiment, the annuloplasty ring is an open ring. The annuloplasty ring has the desired configuration of the mitral or tricuspid valve annulus. In one preferred embodiment, the shape-memory material is selected from a group consisting of shape-memory Nitinol, shape-memory plastic, or the like.
The shape-memory material may be embedded within a biocompatible substrate selected from a group consisting of silicone, polyurethane, expanded polytetrafluoroethylene, semi-permeable material, elastomer, mixture of said biocompatible substrate thereof, and the like. The embedding may make the annoloplasty ring impermeable to blood and provide supportive strength. Furthermore, an internal space of the fabric sheath may comprise a therapeutic agent selected from a group consisting of heparin agent, virucidal agent, anti-ulcer agent, anti-inflammatory agent, antibiotics, anti-cancer agent, and mixture of said therapeutic agent thereof.
In another preferred embodiment, the shape-transition temperature for the shapememory material is preferably between about 39xc2x0 C. and about 90xc2x0 C. The shape-transition temperature is further preferred at a temperature region that is sufficient to cause the shape-memory material to transform to its preshape but not too high to undesirably affect the tissues. The source of heat for heating the shape-memory material to above the shape-transition temperature may be selected from a group consisting of radiofrequency energy, heated balloon, infrared energy, ultrasound energy, and laser energy. Alternately, the source of heat may comprise an external magnetic circuit or other remote source.
The fabric sheath may be stretchable or distensible to accommodate the distension of the annuloplasty ring at a later time. In a further embodiment, the fabric sheath may be impermeable to prevent blood from entering into the inner spaces. It may also comprise a silicone layer so that the annuloplasty ring is substantially impermeable to blood or blood components. The silicone layer may be placed between the fabric sheath and the inner circular members of the annular ring. The fabric sheath may be suturable to facilitate suturing-in-place of the ring to the surrounding anatomical tissue. The fabric sheath may be made of Dacron or other biocompatible material.
In accordance with another embodiment of the invention, the expandable annuloplasty ring for implantation in a heart valve annulus may comprise a fabric sheath and a plurality of stenting elements mounted within the fabric sheath, wherein each of the plurality of stenting elements is made of shape-memory material having a preshape and its own shape-transition temperature, wherein each shape-memory material expands to its preshape when that shape-memory material is heated to above its own shape-transition temperature.
In still another embodiment, there is provided a method for radially expanding an expandable annuloplasty ring implanted in an annulus of a heart valve of a patient. The method may comprise the steps of implanting within the annulus an expandable annuloplasty ring having a fabric sheath and at least one stenting element mounted within the fabric sheath, wherein the at least one stenting element is made of shape-memory material. Subsequently, after predetermined time duration, apply heat for radially expanding the annuloplasty ring to a size larger than the size at implantation, wherein the shape-memory material expands to its preshape when the shape-memory material is heated to above the shape-transition temperature.